<!-- 换肤 -->
<template>
    <div title="换肤">
      <el-color-picker v-model="theme" class="theme-picker" popper-class="theme-picker-dropdown" size="default"/>
    </div>
  </template>
  
<script>
  import elePlus from "element-plus/package.json";
  const version = elePlus.version; // element-ui version from node_modules
  const ORIGINAL_THEME = "#409EFF"; // default color
  export default {
    data() {
      return {
        chalk: "", // content of theme-chalk css
        theme: ORIGINAL_THEME,
      };
    },
    watch: {
      theme(val, oldVal) {
        if (typeof val !== "string") return;
        const themeCluster = this.getThemeCluster(val.replace("#", ""));
        const originalCluster = this.getThemeCluster(oldVal.replace("#", ""));
        const getHandler = (variable, id) => {
          return () => {
            const originalCluster = this.getThemeCluster(
              ORIGINAL_THEME.replace("#", "")
            );
            const newStyle = this.updateStyle(
              this[variable],
              originalCluster,
              themeCluster
            );
            let styleTag = document.getElementById(id);
            if (!styleTag) {
              styleTag = document.createElement("style");
              styleTag.setAttribute("id", id);
              document.head.appendChild(styleTag);
            }
            styleTag.innerText = newStyle;
          };
        };
        const chalkHandler = getHandler("chalk", "chalk-style");
        if (!this.chalk) {
          const url = `https://unpkg.com/element-plus@${version}/theme-chalk/index.css`;
          this.getCSSString(url, chalkHandler, "chalk");
        } else {
          chalkHandler();
        }
        const styles = [].slice
          .call(document.querySelectorAll("style"))
          .filter((style) => {
            const text = style.innerText;
            return (
              new RegExp(oldVal, "i").test(text) && !/Chalk Variables/.test(text)
            );
          });
        styles.forEach((style) => {
          const { innerText } = style;
          if (typeof innerText !== "string") return;
          style.innerText = this.updateStyle(
            innerText,
            originalCluster,
            themeCluster
          );
        });
        setTimeout(() => {
          ElMessage.success("换肤成功");
        }, 1);
      },
    },
    methods: {
      updateStyle(style, oldCluster, newCluster) {
        let newStyle = style;
        oldCluster.forEach((color, index) => {
          newStyle = newStyle.replace(new RegExp(color, "ig"), newCluster[index]);
        });
        return newStyle;
      },
      getCSSString(url, callback, variable) {
        const xhr = new XMLHttpRequest();
        xhr.onreadystatechange = () => {
          if (xhr.readyState === 4 && xhr.status === 200) {
            this[variable] = xhr.responseText.replace(/@font-face{[^}]+}/, "");
            callback();
          }
        };
        xhr.open("GET", url);
        xhr.send();
      },
      getThemeCluster(theme) {
        const tintColor = (color, tint) => {
          let red = parseInt(color.slice(0, 2), 16);
          let green = parseInt(color.slice(2, 4), 16);
          let blue = parseInt(color.slice(4, 6), 16);
          if (tint === 0) {
            // when primary color is in its rgb space
            return [red, green, blue].join(",");
          } else {
            red += Math.round(tint * (255 - red));
            green += Math.round(tint * (255 - green));
            blue += Math.round(tint * (255 - blue));
            red = red.toString(16);
            green = green.toString(16);
            blue = blue.toString(16);
            return `#${red}${green}${blue}`;
          }
        };
        const shadeColor = (color, shade) => {
          let red = parseInt(color.slice(0, 2), 16);
          let green = parseInt(color.slice(2, 4), 16);
          let blue = parseInt(color.slice(4, 6), 16);
          red = Math.round((1 - shade) * red);
          green = Math.round((1 - shade) * green);
          blue = Math.round((1 - shade) * blue);
          red = red.toString(16);
          green = green.toString(16);
          blue = blue.toString(16);
          return `#${red}${green}${blue}`;
        };
        const clusters = [theme];
        for (let i = 0; i <= 9; i++) {
          clusters.push(tintColor(theme, Number((i / 10).toFixed(2))));
        }
        clusters.push(shadeColor(theme, 0.1));
        return clusters;
      },
    },
  };
  </script>
  
  <style>
  .theme-picker .el-color-picker__trigger {
    vertical-align: middle;
  }
  
  .theme-picker-dropdown .el-color-dropdown__link-btn {
    display: none;
  }
  </style>